No Phone for 30 Minutes Before Bed: What a Four-Week Trial Found

The advice to stop using your phone before bed is everywhere, but trials that test it are rare. A small one from Shanghai asked a simple question: if people who sleep badly stop using their phones for the last half hour before bed, does anything change in four weeks?

What the researchers did

The study, by Jing-wen He, Zhi-hao Tu, Lei Xiao, Tong Su and Yun-xiang Tang of the Second Military Medical University in Shanghai, was published in PLOS ONE in 2020 as a randomized pilot trial.

They recruited students at their university in April 2019. To take part, students had to sleep poorly (a score above 5 on the Pittsburgh Sleep Quality Index, a standard questionnaire) and have the habit of using their phone for more than 30 minutes at bedtime. People with sleep disorders, sleep medication, depression and some other conditions were excluded. The 38 who took part were about 21 years old on average, and most were men.

Half were randomly assigned to stop using their phone for 30 minutes before their usual bedtime, for four weeks. The other half got no instructions. The rule was enforced, not just suggested. On Huawei and Apple phones, which 17 of the 19 used, the researchers set up the phone's screen time controls with a bedtime schedule and a password, so the screen turned grey and apps wouldn't open. Those with other phones were asked to switch them off at the cutoff; the researchers sent a reminder ten minutes before it and phoned people afterward to check that the phones were off.

Everyone kept a sleep diary for a week before and after, and filled in questionnaires on sleep quality, how keyed up they felt at bedtime (the Pre-sleep Arousal Scale) and their mood. They also took a working memory test, the n-back task.

What they found

They fell asleep faster. In the phone-free group, the time it took to fall asleep dropped from about 31 to 18 minutes, against a change from 29 to 27 minutes in the control group.

They slept longer and rated their sleep better. Average sleep in the phone-free group rose from 6.2 to about 6.6 hours, while the control group's fell slightly. Their sleep quality score improved from about 10 to under 6, against a drop from about 9.6 to 8.6 in the control group (lower is better).

Bedtime felt calmer. Both the physical and the mental side of pre-sleep arousal (a racing heart, a racing mind) fell in the phone-free group.

Mood and memory improved too. Positive mood rose compared with the control group, negative mood eased over the four weeks, and accuracy on the harder versions of the working memory test was better than the control group's at the end.

What the study can't tell you

This was a pilot with 38 people, and the authors say no formal sample size was calculated. Sleep was measured with a diary and questionnaires, not with a sleep tracker. The participants were motivated: everyone agreed that bedtime phone use was hurting their sleep and wanted to cut it, and they knew which group they were in. Most were young men at a military medical university in China, so the results may not carry over to everyone. And the researchers enforced the rule with locks, reminders and calls, which a person at home doesn't have.

What it means for your phone

The last half hour is a small, specific change, and in this trial it moved sleep in four weeks. The part that's easy to miss is how the rule was kept: a lock with a password, a reminder and someone checking.

• Pick a cutoff time, 30 minutes before you usually go to sleep.
• Charge the phone away from the bed, so the end of the rule is a walk, not a reach. Our guide to turning your smartphone into a dumb phone has the other settings that help.
• Make the rule hold on a tired night. Unrotten can protect your evenings with its Calmer evenings goal, a window each day when the apps you choose stay locked behind Apple's Screen Time shield.

If you scroll late even when you're tired, our guide to revenge bedtime procrastination explains why, and what helps.